1. Field of the Invention
THE PRESENT INVENTION relates to a triggering unit and more particularly relates to a triggering unit configured to trigger or control the actuation deployment of a safety device in a motor vehicle.
2. Description of Related Art
It has been proposed to provide many safety devices in motor vehicles such as air-bags and safety-belt pretensioners. It is necessary to provide a triggering device to trigger such a safety device at an appropriate instant during an accident situation. In recent years many safety devices have been developed which may be deployed in different modes, depending upon the severity of the crash. For example, the amount of gas injected into an air-bag or the tension applied to a safety belt pretensioner may be selected in dependence upon the severity of the crash. Therefore a triggering arrangement should ideally be able to trigger a safety device and also should be able to control or adapt the deployment or actuation of the safety device so that the safety device is deployed or actuated in an appropriate manner depending upon the severity of the crash.
When a crash detector system only has to determine whether a safety device should or should not be actuated or deployed, a single sensor could be utilised in the form of a central accelerometer. The signal derived from the accelerometer indicates the degree of deceleration of the vehicle, and thus this signal is used to control the deployment of the safety device.
With a single central accelerometer it is exceedingly difficult to determine the severity of a crash before the time which the safety device should be actuated or deployed. It is more common now to use safety systems where the severity of the crash must be determined and the designers of these systems have determined that a single central accelerometer is not sufficient. It has been proposed to use an additional accelerometer, or, alternatively, to use some sort of “radar” mounted in the front of the vehicle to determine the relative speed between the vehicle and an object with which the vehicle is going to collide just before the collision. The radar may be a doppler radar or may be an ultrasonic radar.
When a system of this type is utilised, the threshold change in velocity necessary for deployment or actuation of the safety device may be adjusted in dependence upon the measured relative speed between the vehicle and the object with which there is to be a collision. The present invention seeks to provide an improved triggering unit which may provide an enhanced operating characteristic.